1. Technical Field
The present disclosure relates to electrosurgical instruments used for open and endoscopic surgical procedures for sealing, fusing, or dividing tissue. More particularly, the present disclosure relates to bipolar forceps for sealing vessels, vascular tissues and soft tissues having a blade assembly that is designed to transect tissue while limiting movement of the cutting element.
2. Background of the Invention
Electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate and/or cauterize vessels or tissue. However, certain surgical procedures may require sealing blood vessels or vascular tissue rather than just simply effecting hemostasis. “Vessel sealing” or “Tissue Fusion” is defined as the process of liquefying the collagen, elastin and ground substances in the tissue so that it reforms into a fused mass with significantly reduced demarcation between the opposing tissue structures. In contrast, the term “cauterization” is defined as the use of heat to destroy tissue (also called “diathermy” or “electrodiathermy”) and the term “coagulation” is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. Coagulation of small vessels is usually sufficient to permanently close them. Larger vessels or tissue need to be “sealed” to assure permanent closure. During sealing procedures, surgeons may also divide sealed tissue to ensure that the surrounding tissue heals properly.
Numerous electrosurgical instruments have been proposed in the past for various open and endoscopic surgical procedures. However, most of these instruments cauterize or coagulate tissue and are normally not designed to provide uniformly reproducible pressure on the blood vessel or tissue that, if used for sealing purposes, would result in an ineffective or non-uniform seal. For example, U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. Nos. 4,005,714 and 4,031,898 to Hiltebrandt, U.S. Pat. Nos. 5,827,274, 5,290,287 and 5,312,433 to Boebel et al., U.S. Pat. Nos. 4,370,980, 4,552,143, 5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern et al., U.S. Pat. No. 5,484,436 to Eggers et al. and U.S. Pat. No. 5,951,549 to Richardson et al., all relate to electrosurgical instruments for coagulating, cauterizing, and cutting vessels or tissue.
Some of these instruments include blade members or shearing members that simply cut tissue in a mechanical and/or electromechanical manner and are relatively ineffective for vessel sealing purposes. Other instruments generally rely on clamping pressure alone to procure proper sealing thickness and are often not designed to take into account gap tolerances and/or parallelism and flatness requirements, which are parameters that, if properly controlled, can assure a consistent and effective tissue seal. For example, it may be difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure alone for either of two reasons: 1) if too much force is applied, there is a possibility that the two poles will touch and energy will not be transferred through the tissue resulting in an ineffective seal; or 2) if too low a force is applied, a thicker less reliable seal is created.
Commonly-owned U.S. application Ser. Nos. PCT Application Serial No. PCT/US01/11340 filed on Apr. 6, 2001 by Dycus, et al. entitled “VESSEL SEALER AND DIVIDER”, U.S. application Ser. No. 10/116,824 filed on Apr. 5, 2002 by Tetzlaff et al. entitled “VESSEL SEALING INSTRUMENT” and PCT Application Serial No. PCT/US01/11420 filed on Apr. 6, 2001 by Tetzlaff et al. entitled “VESSEL SEALING INSTRUMENT” teach that to effectively seal tissue or vessels, especially large vessels, two predominant mechanical parameters must be accurately controlled: 1) the pressure applied to the vessel; and 2) the gap distance between the conductive tissue contacting surfaces (electrodes). As can be appreciated, both of these parameters are affected by the thickness of the vessel or tissue being sealed. Accurate application of pressure is important for several reasons: to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue; to overcome the forces of expansion during tissue heating; and to contribute to the end tissue thickness which is an indication of a good seal.
As can be appreciated, considerable surgical skill is needed to determine what force is necessary and to accurately apply pressure to the treated tissue. In cases where tissue needs to be divided during the sealing process, the surgical difficulty is compounded by the use of blade assemblies that require lengthy movement such as longitudinal axial movement when the lower and upper jaw members are closed during the procedure. The long cutting motions are problematic in that they may lead to undesirable movement of the cutting element resulting in or promoting an inaccurate seal and/or division of tissue.